1. Field of the Invention
The present invention relates to a data transfer device and a liquid crystal display device, and particularly to a data transfer device and a liquid crystal display using the data transfer device in which a data bus is terminated by a terminal resistor.
2. Description of Related Art
As a conventional data transfer circuit, there is known a data transfer circuit having an input/output interface called GTL (Gunning Transceiver Logic) or CTT (Center Tapped Termination) as disclosed in the June, 8-th issue of 1992 (No. 556) of xe2x80x9cNikkei Electronicsxe2x80x9d, issued by Nikkei BP Corporation, pp. 133-144.
The data transfer circuit has signal amplitude of 1V or less which is effective to increase the data transfer speed and reduce power consumption. That is, in the data transfer circuit, the data bus is terminated by a terminal resistor to reduce the amplitude, thereby suppressing the power consumption of AC components which is represented by the product of the capacitance, the square of the amplitude voltage and the frequency and increasing the operating frequency, so that high-speed data transfer can be implemented.
As described above, in a conventional data transfer circuit having an input/output interface such as GTL, CTT or the like, data transfer can be implemented at a higher speed and with lower power consumption as compared with a data transfer circuit having full amplitude of a power source voltage by suppressing the power consumption of the AC components. However, in this circuit, power consumption of DC components occurs due to the terminal resistor.
For example, when the termination voltage is set to 1.5V, the signal amplitude voltage of a data signal line is set to xc2x10.5V with the termination voltage being set at the center thereof and the terminal resistor is set to 50xcexa9, a constant current of xc2x110mA flows in the terminating resistor at all times irrespective of high-level or low-level of the signal. Accordingly, data of the same value is continuously transferred, and as a result, even when the substantial frequency velocity of the data is reduced, it is difficult to suppress the power consumption due to the terminal current which flows stationarily.
Therefore, an object of the present invention is to provide a data transfer device and a liquid crystal display device which can reduce the power consumption in a data bus which is terminated by a terminal resistor.
In order to attain the above object, according to a first aspect of the present invention, there is provided a data transfer device having a data transmitter and a data receiver which are connected to each other by a plurality of data signal lines, each data signal line being terminated by a terminal resistor, wherein the data transmitter includes hold signal generating means for generating a hold signal which becomes valid when data to be transmitted are equal to data one cycle before, and stops the data transmission on the basis of the hold signal and transmits the hold signal to the data receiver, and wherein the data receiver includes hold means for holding the data thus received, and stops the reception of the data from the data transmitter on the basis of the hold signal and outputs the data held by the hold means.
According to the first aspect of the present invention, the current flowing in the terminal resistor can be reduced, and thus the power consumption can be reduced.
In the above data transfer device, the hold signal generating means may compare data to be transmitted with data delayed by a predetermined time, and generate the hold signal when these data are coincident with each other. Accordingly, the current flowing in the terminal resistor can be further reduced irrespective of coincidence between the data to be transmitted and the data one cycle before.
Further, in order to attain the above object, according to a second aspect of the present invention, there is provided a liquid crystal display device including a controller and a liquid crystal driving device which are connected to each other by a plurality of data signal lines, and a liquid crystal panel which is driven by the liquid crystal driving device to display information, each of the data signal lines being terminated by a terminal resistor, wherein the controller includes hold signal generating means for generating a hold signal which becomes valid when data to be transmitted are equal to data one cycle before, and stops the data transmission on the basis of the hold signal and transmits the hold signal to the liquid crystal driving device, and wherein the liquid crystal driving device includes hold means for holding data received, and stops reception of the data from the controller on the basis of the hold signal and outputs the data held by the hold means.
According to the second aspect of the present invention, the current flowing in the terminal resistor can be reduced and thus the power consumption can be reduced.
In the above liquid crystal display device, the hold signal generating means may compare data delayed by a predetermined time with data to be transmitted, and generate the hold signal when these data are coincident with each other. Accordingly, the current flowing in the terminal resistor can be reduced irrespective of the coincidence between the transmission data and the data one cycle before.
In the above embodiment, for invalid display data in valid display data and invalid display data, the controller transmits first data and stops transmission of the remaining data to transmit the hold signal to the liquid crystal driving device. Accordingly, the current flowing in the terminal resistor can be reduced during the transmission of the invalid display data.
In the above embodiment, the controller divides the plural data signal lines into plural sets, and a plurality of hold signal generating means are provided in connection with data to be transmitted onto the data signal lines of each set, thereby reducing the current flowing in the terminal resistor of each set.